Grand pianos for many years have been provided with three pedals. The rightmost pedal is a sustaining pedal, sometimes known as a forte pedal. This pedal is connected to mechanism which, upon depression of the pedal, retracts all of the dampers of the piano, whereby all notes played will have a maximum sustain. Similar pedals and mechanisms are conventionally provided on upright pianos.
The leftmost or soft pedal in a grand piano effects movement of the keyboard and actions a slight distance to one side so that only two of the three strings are struck in the middle and treble section, and only of the two in the bichord section. In an upright piano the hammers are simply lifted somewhat closer to the strings so that velocity is reduced.
Most grand pianos have a third center pedal, sometimes known as a sostenuto pedal. By the use of this pedal a note or notes pressed down before the pedal is depressed may be sustained after the fingers have left the keys. There is no effect on subsequently played notes. Some upright pianos have a center third pedal producing a true sostenuto action, however, most upright pianos having a third center pedal do not produce a true sostenuto action. Usually, when the third center pedal is provided on an upright piano it simply provides bass sustain or is a dummy.